Brazing-bonding technology will be described hereinafter in brief. Brazing is performed in a temperature range below the melting point of base metals, to be bonded with each other, at a working temperature of 450° C. or more. The brazing features that a filler metal melted by means of brazing permeates between the two base metals, which face each other, to bond the base metals with each other, and in this instance, the base metals are not transformed.
In the brazing-bonding technology, a property indicating a degree of bonding affinity between two base metals and the filler metal is called wetting, and a phenomenon that the filler metal flows between the base metals to be bonded with each other is called capillary.
To improve the bonding affinity to the base metals, for the filler metal, alloy including silver, copper, zinc, cadmium, phosphorus, nickel, manganese, tin, aluminum, silicon, lead and the like is selected in consideration of kinds and the melting point of the base metals.
The selected filler metal is used as a bonding material for bonding the two base metals with each other during the brazing work. The filler metal generates an oxide while being melted, and flux such as borate, alkaline, chloride, borax and boron is used to prevent the oxide, directly dissolve unnecessary materials, promote removal of the unnecessary materials, or prevent generation itself of the unnecessary materials.
The flux has the following functions. First, the flux dissolves or absorbs the oxide, which remains on the surface of a brazing product or is generated during heating. Second, the flux restrains oxidation of the surface of the base metal during heating. Third, the flux keeps a clean state of the surface of the base metal during the brazing work to increase a fluidity of the filler metal. Moreover, the flux indicates temperature for brazing or increases wetting of the filler metal.
The flux is manufactured in various states of liquid, powder and paste, and may be used separately from the filler metal during the brazing work or used as a compound in which the flux is compounded with the filler metal.
As kinds of the compound, there are a flux coated alloy in which the flux is coated on the outer surface of the alloy selected as the filler metal, a flux cored alloy in which the powdered fluxis injected into the alloy selected as the filler metal, and a flux mixed alloy in which the filler metal and the flux are mixed with each other.
Particularly, as shown in FIG. 6, a flux cored alloy filler metal 200 according to a prior art is manufactured by the steps of injecting a powdered flux 51 into a wire type filler metal 90 and rolling the filler metal 90. So, the flux cored alloy filler metal according to the prior art entails a problem in that a joint 93 is inevitably formed and so the powdered flux 51 may be continuously leaked from the joint 93.